Method for the preservation of timber products

ABSTRACT

A method of treating wood by impregnation of the wood with wood-treating-compositions containing compounds which contain elements selected from copper, chromium and arsenic (CCA) and oxyalkylene polymer additives provides improved properties to the treated wood, better control of oxyalkylene polymer distribution, and reduced leaching of the CCA.

This application is a continuation-in-part of application Ser. No.116,056, filed Sep. 02, 1993, now U.S. Pat. No. 5,460,751.

BACKGROUND OF THE INVENTION

This invention relates to compositions useful for preserving timberproducts. The timber products to which the present invention is directedare typically foundation piles, utility poles, posts, fences, decks,railroad ties, marina structures and other types of products subject todecay due to insect pests, fungi and weathering. The compositions of theinvention provide improved wood-treating solutions having enhancedstability when compared to conventional CCA type solutions. In addition,these compositions, when used to preserve wood products, retard thehardness usually associated with CCA type solutions, resulting in lesscracking and improved climbability.

The two main types of preservatives used to treat timber productsinclude oil-based preservatives such as coal tar creosote, solutions ofcreosote with coal tar or petroleum oils, and solutions of preservativechemicals, such as pentachlorophenol dissolved in a suitable organiccarrier; and water-based preservatives such as acid copper chromatesolution (ACC), chromated copper arsenate solution (CCA) and ammoniacalcopper arsenate solution (ACA). CCA solutions are preferred since theychemically react in the wood to form compounds which are toxic to bothfungi and insects.

However, CCA solutions have been known to impart undesirablecharacteristics to treated wood such as hardening due to chemicalfixation of Cr (VI) in the wood, and various attempts have been made toimprove CCA type wood-treating solutions to increase softness of thetreated wood. In addition, the use of reducing agents or other additivesin CCA solutions tends to raise the pH of the solution above about 2,causing premature precipitation of chromated copper arsenate fromwood-treating solutions prior to or during use, resulting inunacceptable treated products and significant costs associated withwaste disposal or replacement of the solutions.

U.S. Pat. No. 4,567,115 describes a method of treating wood, comprisingthe step of exposing wood to an aqueous solution consisting essentiallyof water, hexavalent chromium, copper, arsenic and polyethylene glycol.In a particular embodiment, a 10% concentration of 1000 molecular weightpolymer of ethylene glycol (PEG 1000) is added to the standard dilutedCCA solution in a manner so that a stable solution is obtained. Theuseful range of PEG solutions is described as being in the 500 to 2000molecular weight range.

U.S. Pat. No. 4,847,002, issued to the same inventor of the abovepatent, describes another attempt at improving the stability of CCA-typesolutions. The patent describes a wood preservative solution comprisinga CCA-type formulation diluted with water and an added amount offluoride ion sufficient to stabilize the solution against precipitationwithout retarding conversion of hexavalent chromium to trivalentchromium in the wood matrix. The patent also claims a wood preservingsolution further consisting essentially of polyethylene glycol. Themolecular weight range of the polyethylene glycol is between 100 and2000, in particular 500 to 2,000 and more particularly 1,000.

Advances have been made in improving CCA solutions. However, problemsassociated with stability of these solutions still exists. In addition,resistance to the use of utility poles treated with CCA persists due toproblems associated with hardness of the treated wood and resultingproblems associated with cracking of CCA treated wood.

The need exists for stable wood preservative solutions which combine thepreservative properties of CCA type solutions with the ease of climbingassociated with oil-based solutions, and methods for the utilization ofsuch solutions.

SUMMARY OF THE INVENTION

The present invention relates to improved methods for application ofaqueous wood-treating compositions containing compounds which containelements selected from copper, chromium and arsenic (hereinaftercollectively referred to as CCA solutions), and oxyalkylene polymeradditives which improve the stability of the solutions. The oxyalkylenepolymer additives of the present invention provide improved stability ofwood-treating solutions by reducing the rate of formation of solidprecipitates, thereby reducing costs associated with rejected treatedproducts and waste disposal costs for destabilized solutions containingprecipitates.

The oxyalkylene polymer additives of the present invention also retardhardening of the treated wood, thereby reducing cracking and improvingclimbability for poles treated with the solutions.

In a preferred embodiment, the wood-treating solutions comprise aqueousCCA solutions containing high molecular weight oxyalkylene polymeradditives having hydroxyl numbers of 45 or less. A preferred group ofoxyalkylene polymer additives include polyethylene glycols or chemicallymodified polyethylene glycols having molecular weights of 2,000 orhigher, and having hydroxyl numbers of 45 or less.

In another embodiment, the wood-treating solution comprises an aqueousCCA solution containing, as the oxyalkylene polymer additive, polymersbased on ethylene oxide (EO) and propylene oxide (PO) monomers in ratiosof 1:1 or greater, having hydroxyl numbers of 45 or less. In a preferredembodiment, the EO and PO monomers are in ratios of 1:1. Ratios of lessthan 1:1 EO:PO are also useful if used in a two-step treating process.

In accordance with another embodiment, the wood-treating solutionscomprise aqueous CCA solutions containing, as the oxyalkylene polymeradditives, a mixture of the above described polyethylene glycols ormodified polyethylene glycols, with the above described ethylene oxide(EO) and propylene oxide (PO) monomers. The mixture of additives ispreferably in a ratio of 3:1 of the polyethylene glycols to EO:POpolymers.

Also provided are wood products produced by a process comprisingtreating wood with an aqueous wood-treating solution comprising a CCAsolution and at least one oxyalkylene polymer additive having a hydroxylnumber of less than about 45.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, aqueous wood-treatingsolutions formulated with compounds containing elements selected fromcopper, chromium and arsenic (hereinafter collectively referred to asCCA solutions) are stabilized by the addition of oxyalkylene polymeradditives having a hydroxyl number of about 45 or less. Suitableoxyalkylene polymer additives include polyethylene glycol, modifiedpolyethylene glycol, ethylene oxide (EO) and propylene oxide (PO)monomers, and mixtures thereof; which when added to the woodtreatingsolutions, provide improved stability of the solutions and retard thehardening effects associated with CCA solutions..

Examples of preferred aqueous wood-treating solutions useful in thepractice of the present invention include Chromated Copper Arsenate(CCA) Types A, B and C. CCA-Type A contains about 16.0-20.9% copperoxide, about 59.4-69.3% chromium as chromic acid and about 14.7-19.7%arsenic as arsenic pentoxide; Type B contains about 18.0-22.0% copper ascopper oxide, about 33.0-38.0% chromium as chromic acid and about42.0-48.0% arsenic as arsenic pentoxide; and Type C contains about17.0-21.0% copper as copper oxide, about 44.5-50.5% chromium as chromicacid, and about 30.0-38.0% arsenic as arsenic pentoxide.

Basic CCA standard solutions (American Wood Preservers' AssociationStandard C4) are well known in the art and are commercially available asconcentrated solutions containing from about 45% to 75% active oxides inwater. The most common commercially used CCA solution is a 50% aqueoussolution containing 23.75% CrO₃, 9.25% CuO and 17% As₂ O₅.

The commercial solutions are normally diluted with water to yieldwood-treating solutions containing about 1% to about 10% active oxides.The more preferred concentration for use in the present invention isfrom about 2% to about 3% CCA in an aqueous solution, most preferablyabout 2.5% aqueous CCA.

In accordance with the present invention, CCA solutions which contain,as the oxyalkylene polymer additive, polyethylene glycols (PEGs) ormodified polyethylene glycols (mPEGs) having hydroxyl numbers of about45 or less, contribute to improved stability of CCA solutions containingthese additives.

Polyethylene glycols (PEGs) are a family of linear polymers formed bythe addition reaction of ethylene oxide and are typically represented bythe formula:

    HO--(CH.sub.2 CH.sub.2 O).sub.n --H

where n is a positive number and represents the average number ofrepeating oxyethylene groups. Polyethylene glycols are normallydesignated with a number that represents its average molecular weight.For example, PEG 8000 consists of a distribution of polymers of varyingmolecular weight with an average molecular weight of 8,000, having anaverage number of repeating oxyethylene groups (n) of 181≧.

Preferred PEGs include those having molecular weight greater than 2,000with hydroxyl numbers less than about 45, and most preferred PEGs arethose having molecular weights in the range of from about 8,000 to about100,000 or higher, and hydroxyl numbers of about 45 or less.

Another type of PEG useful in the present invention are chemicallymodified polyethylene glycols (mPEGs). Typically, mPEGs are prepared byreplacing the terminal hydrogen of a hydroxy group of a PEG with, butnot limited to, linear or branched C₁ -C₁₈ alkyl or aryl groups. Forexample, a methyl modified polyethylene glycol would be represented bythe following formula:

    CH.sub.3 O--(CH.sub.2 CH.sub.2 O).sub.n --H

where n is a positive number and represents the average number ofrepeating oxyethylene groups. Preferred groups for modifying PEGs byreplacing the terminal hydrogen of a hydroxy group include methyl, ethyland butyl. Again, the mPEGs have hydroxyl numbers less than about 45. Amost preferred group of mPEGs are those based on replacement of theterminal hydrogen of a hydroxy group of the PEG with a methyl group.Suitable methods for producing methoxy mPEGs are well know in the artand may use compounds such as methanol, methyl cellusolve, methylcarbitol, and the like. Again, mPEGs are designated by a numberrepresenting the average molecular weight, such as CARBOWAX® MPEG 5000,a registered trademark of Union Carbide Corporation for a methylmodified polyethylene glycol having a molecular weight of 5,000.Hereinafter, the term "PEG" will include PEGs and mPEGs.

Another class of compounds useful as oxyalkylene polymer additives inaqueous CCA solutions include polymers based on ethylene oxide (EO) andpropylene oxide (PO) monomers, represented by the following generalformula: ##STR1## where R and R' can be hydrogen or an organicsubstituent having from 1 to 12 carbon atoms, preferably 1 to about 4carbon atoms. Preferably, the organic substituents encompassed by R andR' are linear or branched alkyl groups. In addition, R', which endblocks or caps the EO:PO polymer backbone, can comprise an ether orester linkage. The subscripts m and n have a value of zero or a positivenumber, provided the sum m+n is a positive number, typically notexceeding 1,000.

Methods for preparing the oxyalkylene polymers based on EO and POmonomers for use in the practice of the present invention are known tothose skilled in the art. In addition, the starting materials, e.g.ethylene oxide, propylene oxide, butanol, glycerol and hydrogen, arecommercially available.

The polymers based on EO:PO can be homopolymers, copolymers orterpolymers. The copolymers or terpolymers can be random, blocked orbranched. The oxyethylene and oxypropylene units can be present in anyorder or sequence, and mixtures of various ratios of EO:PO polymers canbe employed in the present invention. In a more preferred embodiment,the ratio of ethylene oxide monomers (EO) to propylene oxide monomers(PO) in the oxyalkylene polymer is in the range of from about 1:1 toabout 3:1, with a most preferred ratio of EO:PO being 1:1. Again, theEO:PO oxyalkylene polymers useful in the practice of the presentinvention have hydroxyl numbers less than about 45.

With ratios having higher concentrations of PO present, from less than1:1 EO:PO up to and including 0:1 EO to PO, it may be necessary toexpose the wood to the additive using a process wherein the commercialCCA solution is diluted with water to the desired concentration andapplied using convention techinques, followed by a separate impregnationstep using the EO:PO oxyalkylene polymer additive having higher ratiosof PO. Again, the preferred concentration of oxyalkylene polymeradditives should be in the range of from about 1 to about 20 weightpercent.

In another embodiment, a mixture of the above described PEGs with theabove described EO:PO polymers may be used as the oxyalkylene polymeradditives for aqueous wood-treating solutions. Although the mechanism isnot fully understood, it is believed that an advantage is afforded bymixing the two types of additives. It is believed that the EO:POpolymers penetrate deeper into the wood where they are not readilyleached out; whereas, PEG additives, which tend to remain closer to thesurface of the wood, further prevent the EO:PO polymers from leachingfrom the wood. Although PEGs having molecular weights greater than 2,000and hydroxyl numbers less than about 45 are preferred, when using thesetypes of mixtures, it is also possible to mix lower molecular weightPEGs (i.e. PEGs with molecular weights less than about 2000, e.g. PEG1000) with EO:PO polymers and still obtain improved performance.

Ratios for mixing PEGs with EO:PO polymers can vary over wide rangesdepending on the desired performance characteristics of thewood-treating solutions. For example, it is believed that softnessrequirements may be met by using additive mixtures high in ratios ofEO:PO polymers to PEGs; while it is believed that leaching stabilityrequirements may be met by using higher ratios of PEGs to EO:POpolymers. Preferred ratios for mixtures include ranges of from about10:1 PEG to EO:PO polymer, up to about 1:10 PEG to EO:PO polymer. A mostpreferred ratio is 3:1, PEG to EO:PO polymer.

Any of the above enumerated PEGs and EO:PO polymers may be mixed,however, most preferred mixtures include those containing PEG 1000, mPEG5000, or PEG 8000, mixed with an EO:PO (1:1) polymer, in a ratio of 3:1

The hydroxyl number of any of the oxyalkylene polymer additives used inthe present invention may be determined by methods known in the art. Thehydroxyl number is the number of milligrams of potassium hydroxideequivalent to the hydroxyl content of one gram of the sample, and may bedetermined using conventional analytical techniques when the molecularweight of a compound is unknown, or may be estimated mathematically whenthe molecular weight is known. For example, the following formula may beused to calculate the approximate hydroxyl number of a compound of knownmolecular weight: ##EQU1## For example, PEG 1000, which has an averagemolecular weight of 1,000, and 2 hydroxy groups, would have a hydroxylnumber approximately equal to 110.

Other compounds containing hydroxy groups and having hydroxyl numbers ofless than about 45 may also be used in the practice of this invention,if they are chemically compatible with CCA solutions.

The total amount of oxyalkylene polymer additive used in CCA solutionsgenerally ranges from about 1 to about 20 weight percent, preferablyfrom about 2 to about 15 weight percent, and most preferably from about4 to about 10 weight percent. The oxyalkylene polymer additives may bemade up as 50% solutions which, when added to the a commerciallyavailable 50% CCA solution and diluted with water, result inwood-treating solutions containing the additives at the desired levelsof from about 1 to about 20 weight percent in a 2.5% CCA solution.

As discussed earlier, one of the problems associated with the use of CCAsolutions is that reducing agents or other additives in the CCAsolutions tends to raise the pH of the solution above about 2, causingpremature precipitation of chromated copper arsenate from the solutionsprior to or during use. The oxyalkylene polymer additives of the presentinvention were evaluated to determine their stability in CCA solutions,as measured by change in pH and formation of a solid precipitate.

The CCA/oxyalkylene polymer additive solutions listed below in Table Iare prepared by dissolving 40 grams of the oxyalkylene polymer additivein 910 grams of water prior to addition of 50 grams of an aqueous 50%CCA standard solution, obtained from Osmose Corporation, to make a finalconcentration of 4% additive in 2.5% CCA. The solutions were allowed tosit at room temperature for a period of time until a precipitate beganto form, up to about eight (8) weeks.

The oxyalkylene polymer additives evaluated were obtained from UnionCarbide Corporation and are as follows:

CARBOWAX® PEG 1000 (registered trademark of Union Carbide Corporationfor polyethylene glycol, avg. mol. wt. 1,000; Comparative Example) in2.5% CCA

CARBOWAX® PEG 3350 (registered trademark of Union Carbide Corporationfor polyethylene glycol, avg. mol. wt. 3,350) in 2.5% CCA

CARBOWAX® MPEG 5000 (registered trademark of Union Carbide Corporationfor modified polyethylene glycol with a single methyl group replacingthe hydrogen atom of a hydroxy group at one end of the molecule, avg.mol. wt. 5,000) in 2.5% CCA

CARBOWAX® PEG 8000 (registered trademark of Union (Carbide Corporationfor polyethylene glycol, avg. mol. wt. 8,000) in 2.5% CCA

CARBOWAX® PEG 20M (registered trademark of Union Carbide Corporation forpolyethylene glycol, avg. mol. wt. 20,000) in 2.5% CCA

POLYOX® WSR N-10 (registered trademark of Union Carbide Corporation forpolyethylene glycol, avg. mol. wt. 100,000) in 2.5% CCA

UCON®75H1400 (registered trademark of Union Carbide Corporation forwater started 75:25/EO:PO copolymers, avg. mol. wt. 2,470, viscosity1400 Saybolt Universal Seconds (SUS)) in 2.5% CCA

UCON®50HB5100 (registered trademark of Union Carbide Corporation forbutanol started 50:50/EO:PO copolymers, avg. mol. wt. 3,930, viscosityof 5100 SUS) in 2.5% CCA

UCON®75H90000 (registered trademark of Union Carbide Corporation forwater started 75:25/EO:PO copolymers, avg. mol. wt. 15,000, viscosity90,000 SUS) in 2.5% CCA

                  TABLE I                                                         ______________________________________                                        STABILITY                                                                                                   Vol..sup.b                                                                         pH    pH                                   Additive Hydroxyl # # days.sup.a                                                                            (ml) Initial                                                                             Final.sup.c                          ______________________________________                                        PEG 1000 110        21        5    1.8   2.6                                  (Compa-                                                                       rative                                                                        Example)                                                                      PEG 3350 35         35        3    1.8   2.3                                  MPEG 5000                                                                              11         >56       0    1.8   2.2                                  PEG 8000  8         42        2    1.8   2.2                                  PEG 20M   6         35        3    1.8   2.3                                  WSR N-10  1         >56       0    1.8   2.2                                  75H1400  46         21        4    1.8   2.5                                  50HB5100 15         35        2    1.8   2.3                                  75H90000  8         42        2    1.8   2.2                                  ______________________________________                                         .sup.a number of days when CCA precipitate first appeared                     .sup.b volume of CCA precipitate after 8 weeks                                .sup.c pH of the solution after 8 weeks                                  

In addition to providing improved stability for CCA solutions containingadditives, the oxyalkylene polymer additives of the present inventionhave been found to retard hardening effects associated with CCAsolutions applied to wood. The types of wood that may be treated withthese types of solutions are well known in the art and include red pine,southern yellow pine, jack pine, white pine, loblolly pine, cedar,douglas fir, poplar, beech, oak and the like. The most prevalent typesof wood used in utility pole applications are red pine, southern yellowpine and jack pine.

The wood may be exposed to treatment with the CCA solution containingoxyalkylene polymer additives by one of the various techniques wellknown in the art, such as dipping, soaking, spraying, brushing, fullcell and empty cell pressure impregnation, compression impregnation, andthe like.

The most commonly used technique for treating wood with CCA solutions isa one-step pressure impregnation process whereby the CCA solution andany additive present are mixed prior to impregnation into the wood. Thepressures generally range from about 25 psi to about 200 psi. The timerequired for complete penetration also varies with the species of wood,thickness of wood and pressure, but is typically from about 2 to about12 hours.

In a wood-treating process wherein an additive has limited solubility inaqueous CCA solutions, such as with polymers based on EO:PO monomers inratios having higher concentrations of PO, (i.e. from less than 1:1EO:PO up to and including 0:1 EO:PO), it may be desirable to use morethan one step. For example, in a two-step process, the CCA solution maybe applied first, followed by a short fixation period prior toimpregnation of the desired oxyalkylene additive. Even where theoxyalkylene polymer is not subject to significant solubilitylimitations, it may be desirable to utilize such a two-step processbecause it tends to produce better, or more advantageously controlled,distribution of the oxyalkylene additive. It has also been surprisinglyfound that such a two-step process provides a wood product subject toless leaching out of the CCA, which is desirable from the envirionmentalpoint of view.

In the treatment of hard-to-treat species, such as oak, maple, teak,etc., it may be desirable to utilize a two-step method wherein theoxyalkylene material is impregnated into the wood, optionally followedby an appropriate residence time, before the CCA impregnation isperformed. Without intending to be bound by any particular theory, it isbelieved that the oxyalkylene material serves to bulk the wood and openup the cell walls, thereby allowing better penetration of the CCA forbetter wood preservation.

The rate of absorption varies greatly with different species andtimbers, thus, a particular technique used will be determined by suchfactors as the species of wood treated, the thickness and shape of thewood, the degree of treatment required, and others factors readily knownto one in the art.

Numerous examples have been performed demonstrating the effectiveness ofthis invention. The following examples illustrate the invention, butshould not be construed to limit the same.

EXAMPLES

The hardness of wood is measured by methods known in the art such aspilodyn penetration. Pilodyn penetration is measured as the distance aspike having a particular shape is driven into the wood under apredetermined load. Thus, the depth of penetration of the spike isdirectly proportional to increases in softness.

Logs used for evaluation are red pine (RP) and southern yellow pine(SYP) logs of about 20-35 centimeters in diameter and about 30-180centimeters in length. For each oxyalkylene polymer additive tested, anaqueous solution is prepared by dissolving the additive in water andadding it to the appropriate amount of 50% CCA solution and dilutingwith water to make a final concentration of 4% or 10% additive in 2.5%CCA solution. For example, 3.0 kg of an aqueous 50% CCA solution, 4.8 kgof a 50% solution of the oxyalkylene polymer additive and 52.2 kg ofwater are mixed to prepare a 60 kg wood-treating solution of 4%oxyalkylene polymer additive in 2.5% CCA solution.

Prior to treatment, the logs are prepared by painting each end withEndtite®, a water impermeable sealant, obtained from Coe ManufacturingCompany, to prevent penetration of the treatment solution into the woodthrough cut surfaces. The treatment vessel for a small size log (20cm×30 cm) is a 15-gallon size stainless steel high pressure vesselmanufactured by Dominion Welding Engineering Co., Ontario, Canada. Thetreatment vessel is operated at 150 psig using compressed air and atambient temperature. Logs are treated using the conventional "full cell"method whereby the log is placed inside the pressure vessel, vacuumedunder reduced pressure for about 30 minutes, and pressurized for about 2hours at about 150 psig after introduction of the wood-treatingsolution. After impregnation, excess solution is removed and the entiresystem vacuumed for an additional 30 minutes to complete treatment.After treatment, the logs are allowed to kiln dry at from about 60° C toabout 80° C for up to 40 hours to approximate the original moisturelevel, and then stored at room temperature until use.

EXAMPLE 1

The following oxyalkylene polymer additive solutions were evaluated foreffectiveness in reducing hardness of RP and SYP:

2.5% CCA (control)

4% CARBOWAX® PEG 1000 (polyethylene glycol, avg. mol. wt. 1,000,hydroxyl #110;Comparative Example)in 2.5% CCA

4% CARBOWAX® PEG 8000 (polyethylene glycol, avg. mol. wt. 8,000,hydroxyl #8) in 2.5% CCA

10% CARBOWAX® PEG 1000 (polyethylene glycol, avg. mol. wt. 1,000,hydroxyl #110; Comparative Example) in 2.5% CCA

10% CARBOWAX® PEG 8000 (polyethylene glycol, avg. mol. wt. 8,000,hydroxyl #8) in 2.5% CCA

10% CARBOWAX® MPEG 5000 (modified polyethylene glycol with a singlemethyl group replacing the hydrogen atom of a hydroxy group at one endof the molecule, avg. mol. wt. 5,000 hydroxyl #11) in 2.5% CCA

10% UCON®50HB5100 (butanol started 50:50/EO:PO copolymers, avg. mol. wt.3,930, viscosity of 5100 SUS, hydroxyl #15) in 2.5% CCA

                  TABLE IIA                                                       ______________________________________                                        HARDNESS                                                                      Red Pine                                                                                               %                                                                             Increase                                                            After     in                                                           Initial                                                                              Treatment Softness  % Moisture                                         (mm)   (mm)      (±)    Content                                    ______________________________________                                        CCA       16.4*    14.2*     -13     30-50                                    4% PEG 1000                                                                             16.1*    17.2*      +7     40-50                                    (Comp. Ex.)                                                                   4% PEG 8000                                                                             12.8     18.6      +45     40-50                                    ______________________________________                                         *Data obtained from Trumble & Messina, "CCAPEG Pole Preservation              Research," Proceedings 81st Annual Meeting American WoodPreservers'           Association, p. 203-213 (1985)                                           

                  TABLE IIB                                                       ______________________________________                                        HARDNESS                                                                      Southern Yellow Pine                                                                                   %                                                                             Increase                                                            After     in                                                           Initial                                                                              Treatment Softness  % Moisture                                         (mm)   (mm)      (±)    Content                                    ______________________________________                                        CCA       13.3*    12.0*     -10     30-50                                              8        8           0     15-25                                    4% PEG 1000                                                                             13.3*    11.4*     -14     35-45                                    (Comp. Ex.)                                                                             9        9           0     15-25                                    4% PEG 8000                                                                             14.2     15.7      +11     30-50                                              8        10        +20     15-30                                    10% PEG 1000                                                                            14.2     11.6      -18     30-50                                              12       11         -8     15-30                                    10% PEG 8000                                                                            11       16        +45     15-30                                    ______________________________________                                         *Data obtained from Trumble & Messina, "CCAPEG Pole Preservation              Research," Proceedings 81st Annual Meeting American WoodPreservers'           Association, p. 203-213 (1985)                                           

EXAMPLE 2

From the above, it can be seen that comparative examples using 4% PEG1000 perform better than comparative examples using 10% PEG 1000.Therefore, additional comparisons were made using 4% PEG 1000 as thecomparative example versus oxyalkylene polymer additives of the presentinvention.

                  TABLE IIIA                                                      ______________________________________                                        HARDNESS                                                                      Red Pine                                                                                               %                                                                             Increase                                                            After     in                                                            Initial                                                                             Treatment Softness  % Moisture                                          (mm)  (mm)      (±)    Content                                    ______________________________________                                        CCA        14.0    13.0       -7     20                                       4% PEG 1000                                                                              13.0    14.0       +8     20                                       (Comp. Ex.)                                                                   4% PEG 8000                                                                              13.0    17.0      +31     20                                       10% MPEG 5000                                                                            14.0    20.0      +43     20                                       10% 50HB5100                                                                             14.0    20.0      +43     20                                       ______________________________________                                    

                  TABLE IIIB                                                      ______________________________________                                        HARDNESS                                                                      Southern Yellow Pine                                                                                   %                                                                             Increase                                                            After     in                                                            Initial                                                                             Treatment Softness  % Moisture                                          (mm)  (mm)      (±)    Content                                    ______________________________________                                        CCA        8.0     8.0         0     20                                       4% PEG 1000                                                                              9.0     9.0         0     20                                       (Comp. Ex.)                                                                   4% PEG 8000                                                                              8.0     9.0       +13     20                                       10% MPEG 5000                                                                            11.0    13.0      +18     20                                       10% 50HB5100                                                                             11.0    15.0      +36     20                                       ______________________________________                                    

EXAMPLE 3

By using oxyalkylene polymer additives of the present invention, anadditional advantage is gained in that CCA solutions containing theseadditives resist leaching under harsh conditions including rain and highhumidity.

Both RP and SYP logs are treated with 4% PEG 8000 in 2% CCA solutionsusing the application procedures described above. In addition, acomparative example was run by treating RP with a 4% PEG 1000 in 2% CCAsolution and SYP with a 10% PEG 1000 in 2% CCA solution. After drying,the logs are placed in a conditioning chamber and subjected to six (6)weeks of continuous wetting from water sprinklers (to simulate rain), atroom temperature and controlled humidity of approximately 100%. At theend of this period, the logs are removed from the conditioning chamber,and allowed to kiln dry at about 60° C. to about 80° C. to approximatethe original moisture level.

Samples are taken from the logs prior to leaching and after leaching todetermine the concentration of PEG remaining in the wood. Wood samplesconsists of approximately three (3) gram samples removed by boring to adepth of about 8 cm, at various top, middle, and bottom locations on thewood. The wood samples are then ground and extracted with 100 ml ofwater at 50° C. for 1 hour. The amount of PEG in the wood is determinedby methods known in the art such as High Pressure Liquid Chromatography(HPLC). The results are shown in the following table as weight percentof PEG based on the weight of the sample extracted:

                  TABLE IVA                                                       ______________________________________                                        LEACHING                                                                      PEG 8000 Additive                                                                       Before      After                                                   Wood Type Leaching    Leaching % Retention                                    ______________________________________                                        RP        2.7         2.1      78                                             SYP       2.1         1.9      90                                             ______________________________________                                    

                  TABLE IVB                                                       ______________________________________                                        LEACHING                                                                      PEG 1000 Additive                                                                       Before      After                                                   Wood Type Leaching    Leaching % Retention                                    ______________________________________                                        RP        3.4         2.0      58                                             SYP       8.2         4.7      57                                             ______________________________________                                    

EXAMPLE 4

In another preferred embodiment of the present invention, oxyalkylenepolymer additive mixtures of PEGs with EO:PO polymers are used to treatwood. The procedure of Example 2 was repeated using SYP and a 4%oxyalkylene polymer additive in 2.5% CCA. The following solutions weretested:

2.5% CCA (control)

3% CARBOWAX® PEG 1000+1% UCON®50HB5100 in 2.5% CCA

3% CARBOWAX® MPEG 5000+1% UCON®50HB5100 in 2.5% CCA

3% CARBOWAX® PEG 8000+1% UCON®50HB5100 in 2.5% CCA

                  TABLE V                                                         ______________________________________                                        HARDNESS - MIXTURES OF PEGs and SYNTHETIC                                     EO:PO POLYMERS                                                                SYP                                                                                                    %                                                                             Increase                                                            After     in                                                            Initial                                                                             Treatment Softness  % Moisture                                          (mm)  (mm)      (±)    Content                                    ______________________________________                                        2.5% CCA   8        8          0     8                                        (Control)                                                                     PEG 1000 and                                                                             8       10        +25     10                                       50HB5100 (3:1)                                                                           8       11        +38     8                                        MPEG 5000 and                                                                            8       10        +25     8                                        50HB5100 (3:1)                                                                           8       11        +38     8                                        PEG 8000 and                                                                             8       11        +38     8                                        50HB5100 (3:1)                                                                           8       11        +38     8                                        ______________________________________                                    

What is claimed is:
 1. A method of treating wood comprising the step oftreating said wood with an aqueous wood-treating composition comprisinga chromated copper arsenate (CCA) solution and at least one oxyalkylenepolymer additive having a hydroxyl number of less than about 45 and amolecular weight greater than about 5,000, wherein the oxyalkylenepolymer additive is polyethylene glycols, polymers based on ethyleneoxide and propylene oxide monomers, or mixtures thereof.
 2. A method ofclaim 1 wherein the terminal hydrogen of a hydroxy group of apolyethylene glycol is replaced with a linear or branched C₁ -C₁₈ alkylor aryl group.
 3. A method of treating wood comprising the step oftreating said wood with an oxyalkylene polymer additive having ahydroxyl number of less than about 45 and a molecular weight greaterthan about 5,000 followed by a separate step of treating said wood withan aqueous chromated copper arsenate (CCA) solution.
 4. A method oftreating wood comprising the step of treating said wood with an aqueouschromated copper arsenate (CCA) solution followed by a separate step ofexposing said wood to an oxyalkylene polymer additive having a hydroxylnumber of less than about 45 and a molecular weight greater than about5,000.
 5. A wood product produced by the method of claim
 1. 6. A woodproduct produced by the method of claim
 3. 7. A wood product produced bythe method of claim 4.